Hibernate Interview Questions


 Hibernate Interview Questions






1. What is Hibernate?                                                                                          

      Hibernate is a powerful, high performance object/relational persistence and query service. This lets the users to develop persistent classes following object-oriented principles such as association, inheritance, polymorphism, composition, and collections

 

2.What is ORM ?
ORM stands for Object/Relational mapping. It is the programmed and translucent perseverance of objects in a Java application in to the tables of a relational database using the metadata that describes the mapping between the objects and the database. It works by transforming the data from one representation to another.

3.What are the different levels of ORM quality?                                                                  There are four levels defined for ORM quality.                                                                                  

Ø  Pure relational
Ø  Light object mapping
Ø  Medium object mapping
Ø  Full object mapping

4. How will you configure Hibernate?
The configuration files hibernate.cfg.xml (or hibernate.properties) and mapping files *.hbm.xml are used by the Configuration class to create (i.e. configure and bootstrap hibernate) the SessionFactory, which in turn creates the Session instances. Session instances are the primary interface for the persistence service.

" hibernate.cfg.xml (alternatively can use hibernate.properties): These two files are used to configure the hibernate sevice (connection driver class, connection URL, connection username, connection password, dialect etc). If both files are present in the classpath then hibernate.cfg.xml file overrides the settings found in the hibernate.properties file.

" Mapping files (*.hbm.xml): These files are used to map persistent objects to a relational database. It is the best practice to store each object in an individual mapping file (i.e mapping file per class) because storing large number of persistent classes into one mapping file can be difficult to manage and maintain. The naming convention is to use the same name as the persistent (POJO) class name. For example Account.class will have a mapping file named Account.hbm.xml. Alternatively hibernate annotations can be used as part of your persistent class code instead of the *.hbm.xml files.

5. What are derived properties?
The properties that are not mapped to a column, but calculated at runtime by evaluation of an expression are called derived properties. The expression can be defined using the formula attribute of the element.

6 Define HibernateTemplate?
org.springframework.orm.hibernate.HibernateTemplate is a helper class which provides different methods for querying/retrieving data from the database. It also converts checked HibernateExceptions into unchecked DataAccessExceptions.

7. What are the benefits does HibernateTemplate provide?
The benefits of HibernateTemplate are :
  • HibernateTemplate, a Spring Template class simplifies interactions with Hibernate Session.
  • Common functions are simplified to single method calls.
  • Sessions are automatically closed.
  • Exceptions are automatically caught and converted to runtime exceptions.
8 . What is the difference between sorted and ordered collection in hibernate?
sorted collection vs. order collection :-
sorted collection 
order collection 
A sorted collection is sorting a collection by utilizing the sorting features provided by the Java collections framework. The sorting occurs in the memory of JVM which running Hibernate, after the data being read from database using java comparator. 
Order collection is sorting a collection by specifying the order-by clause for sorting this collection when retrieval. 
If your collection is not large, it will be more efficient way to sort it. 
If your collection is very large, it will be more efficient way to sort it . 


9. What are the Collection types in Hibernate ?
  • Bag
  • Set
  • List
  • Array
  • Map
10. What is Hibernate proxy?
The proxy attribute enables lazy initialization of persistent instances of the class. Hibernate will initially return CGLIB proxies which implement the named interface. The actual persistent object will be loaded when a method of the proxy is invoked


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